1. Field of the Invention
One of the aspects of the present invention relates to a control device and a control method of a five-axis control machine tool including three linear axes and two rotation axes, a program, and a mold.
2. Description of the Related Art
A five-axis control machine tool is a machine tool having two rotation axes in addition to three orthogonal linear axes. For example, the rotation axis of a tilting table is defined to be parallel to any of the three linear axes, and the rotation axis of a rotating table on the tilting table is defined to be parallel to one of the linear axes that are orthogonal to the rotation axis of the tilting table. The tilting table and the rotating table are arbitrarily rotated so that a workpiece placed on the rotating table is inclined in an arbitrary direction. As a consequence, the preparation time is decreased and the machining efficiency is increased.
In the above-described five-axis control machine tool, the rotation axes of the tilting table and the rotating table should be parallel to the linear axes. In reality, however, the rotation axes are often inclined with respect to the linear axes due to the machining errors or installation errors of the tilting table and the rotating table. Further, even though it is desirable that there are no axial runouts of the rotation axes during the rotation, the runouts are caused by the installation errors or the like. On the other hand, an NC-data generation device generates NC data based on the premise that the rotation axes of the tilting table and the rotating table are parallel to the linear axes. Therefore, the position and attitude of a workpiece in the NC data generated by the NC-data generation device may not agree with those of the workpiece which is actually placed on the five-axis control machine tool due to errors including, for example, the inclinations of the rotation axes of the tilting table and the rotating table, and the machining precision may be decreased.
Accordingly, methods for decreasing the influence of the inclination or runouts of the rotation axes on the machining precision by correcting the inclination or runouts have been proposed. For example, as disclosed in Japanese Patent No. 4327894, position-correction amounts are set for a positioning error and an inclination error dependent on the rotation-axis position, and the position-correction amounts are added to a command linear-axis position so that the tool-tip position is moved to a position free from the errors to decrease the influence of the rotation-axis error on the machining precision.
However, the rotation-axis errors including the inclination, runouts, etc. of the rotation axis cause not only the deviation of the machining position, but also the inclination of the workpiece. The inclination of the workpiece occurs not only in the horizontal direction, but also in the vertical direction. Since the method disclosed in Japanese Patent No. 4327894 corrects only the linear-axis position, the vertical inclination of the workpiece is insufficiently corrected and the tool's attitude relative to the workpiece is inclined. As a consequence, stepped cutting marks are formed and the machining precision is decreased.
The invention provides a five-axis control machine tool that can correct an erroneous attitude of a workpiece toward a tool caused by the inclination of rotation axes of the five-axis control machine tool, and increase the machining precision.